1. Field of the Invention
The present invention relates to elevator safety systems. More specifically, the invention relates to an elevator safety system incorporating a false pit for use where circumstances prevent the construction of a standard safety pit.
2. Related Art
The safety code for elevators and escalators (ASME A17.1) requires a "minimum bottom car clearance" above an area with a physically restricted pit depth. Pit depth can be limited by a variety of conditions, including but not limited to pre-existing construction, a building structure, a geological formation such as bedrock, or a locally high water table. Attempting to install a minimum pit depth under these conditions often results in financial burdens which cause the delay or cancellation of installation. Financial burden can result from the need to use explosives to eliminate a large boulder or bedrock. However, in the case of a high water table, there is no solution readily available, except to relocate or redesign the building structure.
Another factor to be considered is the need to meet minimum standards of accessibility for the handicapped or physically impaired. An elevator often will provide the needed accessibility. However, in a pre-existing facility, there may be obstacles to placement of an elevator. One such obstacle is the minimum pit depth to allow for the minimum bottom car clearance.
Among the relevant portions of ASME A17.1 are Rule 106.1(g) of Section 106 and Rules 107.1 and 107.1(d) of Section 107. In summary, these rules require that a cardboard box measuring either 24 inches wide.times.48 inches long.times.24 inches high or 18 inches wide.times.36 inches long.times.42 inches high must fit beneath the car platform frame without contact when the car is at its lowest possible elevation in the hoistway. The full refuge area must be available even if the normal method of suspending the car is absent due to mechanical failure, periodic maintenance, or for scheduled replacement as is done with hoisting ropes.
In a conventional elevator system, rubber bumpers or spring buffers mechanically limit the car's lowest elevation in the hoistway. The height of the refuge area must meet the code specifications when the car is resting on the bumpers or the fully compressed spring buffers. The car frame size measured horizontally left to right and front to rear has a direct bearing on which refuge area is available. A minimal car platform size would mandate a 42 inch high refuge area, while a larger car platform would allow for a 24 inch high refuge area.
The concept of manual catches which rotate into the elevator shaft to prevent the elevator car from descending is well-known, as is the concept of supporting the elevator car on an arm. For example, U.S. Pat. No. 2,053,954 to Lindahl discloses an arrangement in mining elevators in which an arm rotates out into an elevator shaft to hold the car at a specific location. The arm is able to rotate after the elevator has slowed to a predetermined speed and a worker has manually actuated a lever. U.S. Pat. No. 787,258 Austin discloses a protrusion which supports an elevator in the event that the elevator rises above the protrusion and breaks the supporting cable. U.S. Pat. No. 692,888 Moses discloses support arms embedded in the shaft wall which rotate out to support the elevator when it is located at the top of the shaft U.S. Pat. No. 642,448 Holmes discloses a safety device for elevators in which many levers are embedded in the shaft wall, and can rotate out to engage the edge of the elevator car in an emergency situation. U.S. Pat. No. 406,630 Cowie discloses a safety catch for use in the event of overwinding the elevator cable. The safety catch includes a guide with a shoulder which catches the elevator if the base of the car has risen past the top of the shoulder.
However, the primary concern of the above-described patents is either to catch the elevator at the top of the shaft in case of overwinding of the elevator cable, or to hold the car steady at a particular stop. None of them is directed to providing an area of safety at the terminus of the shaft, or teaches or suggests the means to do so.
The ASME A17.1 safety code for elevators and escalators is constantly evolving to keep pace with new technologies, processes and re-examination of the standards with which elevator and escalator installations must comply. Thus, the ASME A17 Cod especifically states: "Where present rules are not applicable or do not describe the product or system, the enforcing authority should recognize the need for exercising latitude and granting exceptions where the product or system is equivalent in quality, strength or stability, fire resistance, effectiveness, durability, and safety to that intended by the present Code Rules." The present invention takes advantage of this provision to provide an elevator safety system under circumstances where a conventional four (4) foot minimum pit depth cannot be achieved due to pre-existing conditions.